Sewing machine with control device for the needle driving motor

ABSTRACT

A sewing machine, and a control device for the needle driving motor comprising an electronic circuit which employs logic gates and at least one capacitor for its working in such a way as to obtain a simple, reliable and cheap control device.

DISCLOSURE OF THE INVENTION

The present invention relates to a sewing machine with a control devicefor the needle driving motor. Sewing machines are provided with a motorwhich, via a kinematic chain, drives with reciprocating movement asewing needle between an extremely high position and an extremely lowposition (hereinafter simply indicated as high and low position). Thesewing machine is usually provided with an external regulator withwhich, when the machine is started by a general external switch, theoperator controls the driving of the motor from a zero speed to amaximum speed. Some types of sewing machines comprise moreoverexternally a needle stop position selector with two positionscorresponding to the stop of the needle respectively in the high and lowposition. These types of sewing machines comprise also an internalswitch which is activated when the operator mechanically disengages thesewing needle from the motor. In the inside of the above-mentioned typesof sewing machines there is present a motor control electronic circuitoperatively connected to the regulator, to the position selector and tothe internal switch. The control circuit also is connected to twoposition sensors operatively connected to the kinematic chain betweenthe motor and the needle. One sensor indicates to the control circuitwhen the needle is in its high position while the other sensor indicatesto the control circuit when the needle is in its low position. Thesesewing machines have four main working conditions:

(1) sewing: the motor controlled by the regulator turns continually,independently from the signals arriving from the position sensors;

(2) needle positioning when the regulator is placed in the zero speedposition of the motor: the motor stops the needle in the position (highor low) indicated by the position selector; when the machine is stoppedit is possible to carry the needle out of position acting manually onthe hand-wheel;

(3) execution of the bobbin winding: the motor is mechanicallydisengaged from the needle and, as known, the motor is only used inorder to wind the thread coming from a spool on the bobbin obviouslyacting on the regulator; in this case the motor stops as soon as theregulator is released;

(4) needle positioning in high or low position: when the machine ismotionless, operating on the position selector, the needle is displacedin one or the other of the two positions.

The control circuit of course operates in such a way that the sewingmachine can give the above-mentioned performances opportunatelycoordinating the various elements with which it is connected. In knownsewing machines this circuit is quite complicated, less reliable andresults in a higher cost for the same circuit and thus of the sewingmachine.

It is an object of the present invention to provide a sewing machinewhich overcomes the above-mentioned drawbacks, i.e., which has a controldevice for the various functions characterized by simplicity,reliability and low cost.

Such object is achieved by means of a sewing machine comprising a motorfor reciprocating a sewing needle between a first and a second extremeposition, a motor speed regulator for obtaining a zero speed and amaximum speed, a switch operated by means adapted to mechanicallydisengage the sewing needle from the motor, a position selector havingat least two positions for controlling the motor in order to stop theneedle at least in the first or in the second extreme position. Themachine further comprises at least first and second sensor means,operatively connected to the position selector, supplying a controlelectric signal respectively when the needle is in the first extremeposition and in the second extreme position, first means being providedof the logic gate type with a first and a second input and an output,which commutate from the first and a second logic condition and viceversa, i.e., a first logic condition in which at its output an electricsignal is present which controls the starting of the motor and a secondlogic condition in which at its output an electric signal is presentwhich controls the stopping of the motor, the first input of said logicgate means being operatively connected to the regulator in such a waythat when the regulator is in its motor starting position, the firstlogic gate means is in its first logic condition and when the regulatoris in its motor stopping position, the first logic gate means commutatefrom one to the other of its two logic conditions according to the logiclevel present at its second input, second means being moveover providedof the logic gate type having a first and a second input and an output,the output of the second means being connected to the second input ofthe first means, the second means commutating from a first to a secondlogic condition and vice versa, the commutation of the second means fromone to the other of its two logic conditions causing the commutation ofthe first means from one to the other of its two logic conditions whenthe regulator is in the motor stopping position, first capacitor meansbeing moreover provided connected to the first input of the logic gatesecond means and operatively connected to the regulator and to theswitch, the first capacitor means being electrically charged when theregulator is in its motor starting position and being electricallydischarged when the switch is in the position corresponding to thedisengagement of the needle from the motor, the first capacitor means,when it is charged, keeping the second logic gage means in conditions ofnon-commutation, one or the other of the first and second sensor means,depending on the position of the selector, being connected to the secondinput of the second logic gate means in such a way as to supply to itthe electric control signal, the electric control signal, when thisregulator is in its motor stopping position, causing the commutation ofthe second logic means from one logic condition to the other in such away as to cause the commutation of the first logic means in the logiccondition corresponding to the stopping of the motor.

In order to understand the characteristics and advantages of the presentinvention, a description of one exemplifying, non-limitative embodimentis hereafter given, illustrated in the accompanying drawing in which isschematically shown the control device for the driving motor of a needleof a sewing machine according to the invention.

The sewing machine referred to in the following description is of thecommon type comprising in its structure a bed from which a standardlaterally rises, and from which, in turn, a bracket arm extends endingwith a head supporting the sewing means needle bar and needle. Such asewing machine is not illustrated in its structure because of being ofthe known type. In the figure only some components of the sewing machineare illustrated. In particular block 20 schematizes the sewing needleand with motor M, which, via an opposite known kinematic chain,reciprocates the needle 20 between an extremely high and an extremelylow position. An external foot rheostat 30 controls the speed of themotor M between a zero value and a maximum value. An external selector40 positions the needle stop in two positions corresponding to the stopof the needle respectively in a high and in a low position. An internalswitch of the known type 50 is operated by means which mechanicallydisengages the needle 20 from the motor M, indicated in the figure withthe block MS: when the needle 20 is disengaged from the motor M theabove-mentioned disengaging means carries the switch 50 in a closedposition.

The figure principally illustrates the device which controls the motor Mon the basis of information coming to it from foot controller 30, fromthe selector 40 and from the switch 50. The device provides principallytwo needle position sensors schematized by means of blocks SA and SB,connected to the selector 40. The sensors SA and SB emit a particularelectric signal, as will be afterward explained, when the needle 20 isrespectively in the high and low position (i.e., the sensor SA for thehigh position and the sensor SB for the low position). Such sensors maybe of the Hall Effect type operatively connected to a shaft comprised inthe kinematic chain connecting the motor M to the needle 20 according toknown art.

A secondary electronic circuit, of known type, is provided for thecontrol of the needle 20, schematized with the block CV, whose input isconnected to the foot controller 30 and whose output is connected to apower amplifier AP which feeds the motor M when the foot controller 30is in a position of a speed of the motor M different from zero (closedposition). The secondary circuit CV does not operate and the motor Mturns at the speed determined by the foot controller 30. When the footcontroller 30 is in the zero speed position of the motor M (openposition), the secondary circuit CV supplies a suitable signal to thepower amplifier AP in such a way that the speed of the motor M is at afixed speed corresponding to a speed of the needle 20 which is muchlower than the operative speeds. The reasons for this will be clarifiedsubsequently. The control device of the motor M provides moreover a setof electronic components operatively connected to the foot controller30, to the selector 40 and through the selector 40 to the sensor SA andSB, to the switch 50 and at last to the secondary circuit CV as shown inthe figure. The above-mentioned electronic components are formed by: aset of logic gates A, B, C, D of the NAND type, with inputs and outputsindicated with the numbers 1-12;

a set of resistances R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ ;

two capacitors C₁ and C₂ ;

two diodes D₁ and D₂ ;

one transistor T.

The circuit of the above-listed electronic components is fed by atension source of +5 volt. The working of the control device will bedescribed hereinafter, illustrated with reference to the four mainconditions of the sewing machine working indicated in the introductorypart of this description.

(1) Sewing

By pressing and thus bringing into a closed position the foot controller30, the transistor T is conducting and establishes a low logic level atthe input 7 of the gate D. An electric signal will be present at theoutput 9 of the gate D (afterwards the word "signal" will be simply usedfor indicating an electric signal) of high logic level (i.e., the output9 will be at high logic level) independently from the logic level of thesignal arriving at the input 8 of the same gate D. The output 9 of thegate D is connected to a particular input of the secondary circuit CV insuch a way that, when a low logic level signal arrives at this input,the power amplifier AP does not feed the motor M and when, on thecontrary, a high logic level signal arrives at the input, the poweramplifier AP feeds the motor M. Thus in the above-described situation,with high logic level signal at the output 9 of the gate D, theamplifier AP feeds the motor M and this last turns at the speeddetermined by the foot controller 30.

(2) Positioning of the needle when the foot controller is released

It must be stated in advance, that in the previous situation thecommutation into conduction of the transistor T brings the input 4 ofthe gate B to a low logic level and thus a high logic level signal willbe present at the output 11 of the gate B. Such high logic level signalcharges the capacitor C₂ through the resistances R₃ and R₄ and the diodeD₂. When the tension voltage level in C₂ overcomes half of the feedtension of the circuit (thus it exceeds +2.5 volt) the gate C presentsat its input 6 a high logic level signal and thus supplies to its output12 a logic level signal depending on the logic level of the signal atits input 5. More particularly, a high logic level signal will bepresent at the output 12 when a low logic level signal will be presentat the input 5 and vice versa.

It must be moreover stated that the needle position sensors SA and SB,one or the other of them, depending on the position of the selector 40,is connected to the input 5 of the gate C, emit a low logic level signalwhen the needle 20 passes into the position detected by them. In all theother positions of the needle 20 a high logic level signal arrives atthe input 5. When the foot controller 30 is released (i.e., carried intothe open position as in the figure), it is first of all to say, aspreviously explained, that through the secondary circuit CV apredetermined speed corresponding to a speed of the needle 20 much lowerthan the normal operative speed is established for the motor M.

The releasing of the foot controller 30 causes the transistor T to notconduct and a high logic level will be present at the input 7 of thegate D and at the input 4 of the gate B. The output 9 of the gate D willbe at a high or low logic level and thus the motor M will turn or notdepending on the logic level of the input 8 of the same gate D. If suchlevel is low the motor M turns, otherwise it will stop. The logic levelat the input 8 of the gate D depends on the logic level of the output 12of the gate C. As already stated, since the logic level at the input 6of such gate C is high due to the action of the capacitor C₂, the logiclevel at the output 12 of the gate C depends only on the logic level ofits input 5 connected, in an illustrative way in the figure, to thesensor SA.

As a consequence of that, until the needle 20 has not reached itssuperior position, a high logic level is present at the input 5 of thegage C. Thus, a low logic level is present at the output 12 of the gateC and at the input 8 of the gate D and as a consequence at the output 9of the gate D there is a high logic level signal, which causes the motorto turn. When the needle 20 reaches its superior position, the sensor SAsupplies a low logic level signal to the input 5 of the gate C. Thus atthe output 12 of the gate C and at the input 8 of the gate D there is ahigh logic level and as a consequence, as also the input 7 of the gate Dis at a high logic level, at the output 9 of the gate D there is a lowlogic level signal which causes the motor M to stop.

Substantially, when the foot controller 30 is released, the needle 20passes from its operative speed to a much lower speed and stops when ithas reached its superior position. The passage of the needle 20 from itsoperative speed to a much lower speed is necessary. In fact if, on thecontrary, it maintained its operative speed, it would not stop in itssuperior position but it would continue to rotate due to the inertia.Obviously if the selector 40 is displaced on the sensor SB, the controldevice works in the same above examined way with the difference that thestopping of the motor M occurs when the needle 20 is in its lowposition. It is to point out that when the foot controller 30 isreleased and thus the transistor T does not conduct, the output 11 ofthe gate B is at a low logic level and thus the voltage on the capacitorC₂ will reduce as this discharges on the resistance R₃ (in the presentoperative condition the switch 50 is open). When such voltage reducesunder half of the feed voltage, at the input 6 of the gate C there is alow logic level and at its output 12 there is therefore a high logiclevel which causes, for what above explained, the stopping of the motorM. Thus, after a certain time from the release of the foot controller30, equal to the discharge time of the capacitor C₂, the motor M andthus the needle 20 stopping anyhow. In any case this discharge time ofthe capacitor C₂ must be such as to permit, anyway, the stop of theneedle 20 either in the high position or in the low position, accordingto the position of the selector 40. In other words, the capacitor C₂must keep in commutation status the gate C until the low logic levelsignal of the position sensor (SA or SB) arrives at the input 5 of thisgate. When the foot controller 30 is released, it is possible to carrythe needle out of position, manually acting on a hand wheel, without themotor M starting.

In fact, as the capacitor C₂ is discharged, at the output 12 of the gate5 there is a high logic level and thus the motor M remains motionless.Obviously, the discharge time of the capacitor C₂ will have to becalibrated in such a way that the voltage at the capacitor C₂ reducesunder half of the feed voltage, immediately after the release of thefoot controller 30 for avoiding that, by displacing the needle 20 fromthe extreme reached position, at the output of the gate C there is a lowlogic level, as its inputs 5 and 6 are at a high logic level, and thusthe motor starts.

(3) Execution of the bobbin winding

By the disengaging means the needle 20 is disengaged from the motor Mand thus the switch 50 commutates in closed position. When the footcontroller 30 is pressed, the control device working is the one alreadyexplained at the point (1) and the motor M causes the needle 20 to moveat the operative speed established by the same foot controller.

When the foot controller 30 is released, the working logic of thecontrol device is that shown at the point (2); in this case, however,the closing of the switch 50 puts in short-circuit the diode D₂,operating the paralleling of the resistances R₃ and R₄ and causes thecapacitor C₂ to discharge very quickly. This means, for what wasdescribed at the point (2), that the motor M, and thus the needle 20,stop when the foot controller 30 is released, as it is required in thisoperative condition of the sewing machine.

(4) Needle positioning in high or low position when the sewing machineis motionless

When the selector 40 is displaced from the position shown in the figure,corresponding to the stop of the needle 20 in high position, to theposition corresponding to the stop of the needle 20 in low position, thefollowing occurs. During the commutation of the selector 40 from oneposition to the other, the capacitor C₁ is charged by the feed source(+5 V) through the resistance R₁ and the diode D₁.

As a consequence both inputs 1 and 2 of the gate A become high and itsoutput 10 becomes low. The output 11, that when the machine ismotionless is low, becomes high and thus the condensor C₂ charges. Whenthe voltage at the capacitor C₂ exceeds half of the feeding circuittension, for what explained at point (2), the motor M starts and causesthe needle 10 to move. When the selector 40 has displaced in theposition corresponding to the stop of the needle in low position,connecting the sensor SB to the input 5 of the gate C, the condensercapacitor C₁ discharges through R₂ and through a mobile contact of theselector 40. This causes the commutation of the gates A and B in theinitial condition, i.e., the output 10 of the gate A becomes again highand the output 11 of the gate B becomes again low. As a consequence thecapacitor C₂ discharges.

However, until the voltage at the condensor C₂ is higher than half ofthe feeding circuit voltage and until the needle 20 is out of its lowposition, as explained at the point (2), the motor M turns. When theneedle 20 reaches its low position and thus the sensor SB supplies thecommutation signal to the gate C or when the voltage at the capacitor C₂reduces under half of the feed voltage, the motor M stops, causing theneedle 20 to rest.

As already stated at point (2) the discharge time of the capacitor C₂must be such as to permit the needle 20 to stop in the predeterminedposition. Thus displacing the selector 40 in the way above indicated,the needle automatically moves in its low position.

From what has been described and illustrated it can be understood howthe control device is simple either as a circuit structure or as aworking mode.

The simplicity assures the reliability of the circuit and permits lowproduction costs for the same. The reliability is increased by the useof logic gates. In fact, as it is known, the characteristics of thebinary working of the logic gates give particular operative reliabilityto a circuit which uses them, permitting, moreover, to avoid thatfluctuation in the feed voltage and in the internal voltage of thecircuit, obviously within certain limits, influencing the working of thesame circuit.

With obvious modifications a position selector with many positions canbe utilized and, correspondingly, also many position sensors, in orderto stop the needle in positions intermediate with respect to the extremepositions already examined. The working principle is completely similarto the one already considered.

We claim:
 1. Sewing machine comprising a motor for reciprocating asewing needle between a first and a second extreme position, a motorspeed regulator for obtaining a zero speed and a maximum speed, a switchoperated by means adapted to mechanically disengage the sewing needlefrom the motor, a position selector having at least two positions forcontrolling the motor in order to stop the needle at least in the firstor in the second extreme position, the machine comprising at least firstand second sensor means, operatively connected to the position selector,supplying a control electric signal respectively when the needle is inthe first extreme position and in the second extreme position, firstmeans being provided of the logic gate type with a first and secondinput and an output, which commutate from a first and a second logiccondition and vice versa, said first logic condition in which at saidoutput an electrical signal is present which controls the starting ofthe motor and a second logic condition in which at said output anelectric signal is present which controls the stopping of the motor, thefirst input of said logic gate means being operatively connected to saidregulator in such a way that when said regulator is in its motorstarting position, said first logic gate means is in its first logiccondition and when said regulator is in its motor stop position, saidfirst logic gate means commutates from one to the other of its two logicconditions according to the logic level present at its second input,second means being moreover provided of the logic gate type having afirst and a second input and an output, the output of said second meansbeing connected to the second input of said first means, said secondmeans commutating from a first to a second logic condition and viceversa, the commutation of said second means from one to the other of itstwo logic conditions causing the commutation of said first means fromone to the other of its two logic conditions when said regulator is inthe motor stop position, first capacitor means being moreover providedconnected to the first input of said logic gate second means andoperatively connected to the regulator and to the switch, said firstcapacitor means being electrically charged when the regulator is in itsmotor starting position and being electrically discharged when theswitch is in the position corresponding to the disengagement of theneedle from the motor, said first capacitor means, when it is chargedkeeping said second logic gate means in condition of non-commutation,one or the other of said first and second sensor means, depending on theposition of the selector, being connected to the second input of saidsecond logic gate means in such a way as to supply to it said electriccontrol signal, said electric control signal, when this regulator is inits motor stop position, causing the commutation of said second logicmeans from one logic condition to the other in such a way as to causethe commutation of said first logic means in the logic conditioncorresponding to the stopping of the motor.
 2. Sewing machine accordingto claim 1, wherein said first capacitor means is discharged when saidregulator is in the stop position of the motor, said position selectorbeing operatively connected to a circuit which charges said firstcapacitor means when said position selector is in an intermediatepositon between its two positions corresponding to the needle stopextreme positions.
 3. Sewing machine according to claim 2, in which saidcircuit includes third logic gate means with a first and a second inputmeans and output means, which commutates from a first one to an otherlogic condition and vice versa, said one logic condition in which atsaid output means there being present an electrical signal which chargessaid first capacitor means, and said other logic condition in which saidoutput reaches an electrical level such as to discharge said firstcapacitor means, the first input of said third logic gate means beingoperatively connected to said regulator in such a way that, when saidregulator is in motor driving position, said third logic gate means isin the one logic condition and, when said regulator is in motor stopposition, said third logic gate means commutates from one to the otherof its two logic conditions, depending from the logic level present atits second input, said second input means being connected to secondcapacitor means charged in the intermediate positions of the selectorand discharged in the two positions of the selector corresponding to theextreme stop positions of the needle, said second capacitor means, whenit is charged, causing the commutation of said third logic gate meansinto its first logic condition and, when it is discharged, causing thecommutation of said third logic gate means into its other logiccondition.
 4. Sewing machine according to claim 1, including transistormeans connecting said regulator to said first logic gate means, saidregulator, according to its driving or stop motor position, piloting thetransistor means either in conducting or in non-conducting position,said transistor means controlling, by its two said positions, the feedof an electrical signal source to said first logic gate means in orderto carry it either into its first logic condition or into thecommutation state from a logic condition to the other one.
 5. Sewingmachine according to claim 3, including transistor means connecting saidregulator to said first and third logic gate means, said regulatorpiloting, according to its position, the transistor means either inconducting position or in non-conducting position, said transistor meanscontrolling, by their two said positions, the feed of an electricalsignal source to said first and third logic gate means in order to carrythem either into their first logic condition or into the commutationstate from a logic condition to the other one.